You could call it frogs' porn - scientists have identified a previously unknown and unusual amphibian mating position dubbed the "dorsal straddle".

The Kama Newtra discovery emerged from observations of the Bombay night frog (Nyctibatrachus humayuni) which lives in the Western Ghats of India, a biodiversity hotspot.

Six mating positions, or "amplexus nodes", are known among the almost 7,000 species of frogs and toads around the world.

But the Bombay night frog does sex differently. While performing the "dorsal straddle", the male sits above his mate's back with his hands and feet grasping or resting on a leaf, branch or tree trunk.

Now comes the X-rated bit. The male releases sperm over the female's back before moving away. The female then lays her eggs, which are fertilised by the sperm trickling down her back.

As a result, there is no actual physical contact between the sexes during egg laying and fertilisation.

In other frogs, the female usually lays eggs while embracing her mate while the male simultaneously releases his sperm.

Lead researcher Professor Sathyabhama Das Biju, from the University of Delhi, said: "This is a remarkable frog with an unprecedented reproductive behaviour , which is unique for a number of reasons. This discovery is fundamental for understanding the evolutionary ecology and behaviour in anuran (frogs and toads) amphibians."

Female Bombay night frogs are also unusual for calling during the breeding season. While all male frogs call to attract mates, female mating calls are known to occur in only 25 species worldwide.

In addition, the researchers found that fights were common between competing male Bombay night frogs.

During the breeding season, the frogs gather in large numbers in vegetation overhanging streams soon after sunset.

Indian night frogs are an ancient group of amphibians which diversified around 70 to 80 million years ago.